Ink system for cure under low-energy conditions

ABSTRACT

UV-curable ink formulations are provided that are capable of being cured under low-energy conditions, such as with a conventional mercury vapor lamp operating at half or less of the lamp&#39;s nominal wattage. Methods for forming a printed ink image on a substrate using the ink are also provided, which permit maintenance of relatively high line speeds while consuming less energy due to the use of lower-wattage lamp settings.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally pertains to UV-curable ink formulationsthat are capable of being cured under low-energy conditions and methodsfor creating a printed ink image on a substrate using the ink. Inparticular, the ink formulations may be cured using conventionalhigh-wattage bulbs operated at half or less of the bulb's nominalwattage.

2. Description of the Prior Art

Traditional UV-curable ink printing systems commonly utilizehigh-wattage bulbs (e.g., greater than 200 W) to deliver the necessaryUV light energy to initiate the free-radical polymerization processesthat result in curing of the ink onto the substrate to which it has beenapplied. The use of bulbs that emit these high energy levels hasheretofore been critical to the prevention of oxygen inhibition duringthe cure process and to facilitate rapid cure times so that pressthroughput can be optimized. However, the use of high-wattage bulbspresents a number of concerns. As can be readily appreciated, the energyusage to operate equipment with high-wattage bulbs is quite high. Apartfrom the energy usage associated with the direct operation of the bulbsthemselves, there are also indirect energy consequences as well. Thesebulbs also tend to emit relatively large amounts of heat energy whenoperated, which may need to be countered with more powerful climatecontrol systems. In addition, the heat energy produced limits theability of the printer to utilize heat-sensitive substrates, such ascertain types of plastics and films that can warp under even fairly mildelevated temperature conditions.

With electrical power grids being taxed to their practical limits,municipalities and utilities often are forced to impose energy caps onbusinesses. In the case of a printer utilizing a large number ofprinting presses with high-wattage bulbs, these caps either mean thatthe printer may encounter limits in production and an inability to growits business through the addition of more printing presses.Consequently, a need exists in the art for an ink system that is capableof curing under exposure to lower-energy conditions without sacrificingline speed.

SUMMARY OF THE INVENTION

The present invention overcomes the problems associated with the use ofhigh-wattage curing equipment by providing UV-curable ink formulations,and methods of printing therewith, that require less energy to fullycure and permit existing equipment to be operated at lower energylevels.

According to one embodiment of the present invention there is provided aUV-curable ink composition comprising a monomer system, an oligomersystem, an acrylate polymer resin, a pigment, and a initiator system.The monomer system comprises at least one monofunctional monomer and atleast one multifunctional monomer. The oligomer system comprises atleast one urethane acrylate oligomer and at least one mercapto modifiedpolyester acrylate. The initiator system comprises at least onephosphine oxide photoinitiator, at least one ketone photoinitiator, atleast one titanocene photoinitator and at least one amine co-initiator.

According to another embodiment of the present invention there isprovided a method for forming an article having a printed ink imagethereon. An ink image is printed onto a substrate using a UV-curable inkcomposition to form a printed substrate. The UV-curable ink compositioncomprises a monomer system comprising at least one monofunctionalmonomer and at least one multifunctional monomer, an oligomer systemcomprising at least one mercapto modified polyester acrylate, and aninitiator system comprising one or more members selected from the groupconsisting of phosphine oxide photoinitiators, ketone photoinitiators,and titanocene photoinitators. The printed substrate is subsequentlypassed through a curing station at a rate of at least 50 linear feet perminute to form the article. The curing station comprises at least onelamp that has a rated wattage of at least 200 W. The lamp is operated at50% or below of its rated wattage while the printed substrate is beingpassed through the curing station.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is generally directed toward UV-curable inkcompositions that can be cured using traditional lamp technology, suchas mercury vapor lamps, operating at a fraction of the lamp's rated(i.e., nominal) wattage. Embodiments of the present invention permitexisting press equipment, equipped with high-wattage lamps, to beoperated at much lower power levels thereby resulting in considerabledirect and indirect energy savings for the press operator. This isaccomplished through the use of an ink composition comprising uniquemonomer, oligomer, and initiator systems that rapidly and completelycure upon exposure to UV light at reduced energy and power levels.

In certain embodiments of the present invention, the monomer systemcomprises at least one monofunctional monomer, at least onemultifunctional monomer, or at least one monofunctional monomer and atleast one multifunctional monomer. In particular embodiments, themultifunctional monomer may be difunctional or trifunctional. In stillfurther embodiments, the mono- and multifunctional monomers compriseacrylates or acrylic monomers. Exemplary acrylic monomers includedipropylene glycol diacrylate monomer (DPGDA), 1,6-hexanedioldiacrylate(HDODA), isobornyl acrylate (IBOA), 2-phenoxyethylacrylate (2-PEA),tripropylene glycol diacrylate (TPGDA), trimethylolpropane triacrylate(TMPTA), tetraethylene glycol diacrylate, and ethoxylated andpropoxylated derivatives of the foregoing. The total monomer content ofthe ink formulation may be from about 20% to about 60% by weight, fromabout 25% to about 55% by weight, from about 30% to about 50% by weight,or from about 35% to about 45% by weight, based upon the total weight ofthe ink formulation. The monofunctional monomers may be present in theink formulation at a level of between about 5% to about 35% by weight,between about 10% to about 30% by weight, or between about 15% to about25% by weight. The total multifunctional monomer content of the ink maybe from about 5% to about 35% by weight, between about 10% to about 30%by weight, or between about 15% to about 25% by weight. Moreparticularly, when the at least one multifunctional monomer comprises adifunctional monomer, the difunctional monomer may be present within theink composition at a level of from about 6% to about 35% by weight, fromabout 10% to about 28% by weight, or from about 14% to about 22% byweight. When the at least one multifunctional monomer comprises atrifunctional monomer, the trifunctional monomer may be present withinthe ink formulation at a level of from about 0.1 to about 10% by weight,from about 0.5 to about 7% by weight, or from about 1% to about 5% byweight.

In certain embodiments, the oligomer system comprises at least one of aurethane acrylate oligomer and a polyester acrylate oligomer. Inparticular embodiments, the oligomer system comprises both a urethaneacrylate oligomer and a polyester acrylate oligomer. In certainembodiments, the urethane acrylate oligomer comprises two or moreoligomers, at least one of which is a difunctional aliphatic urethaneacrylate. Exemplary urethane acrylate oligomers include EBECRYL 8811from Allnex and CN 983 from Sartomer. The urethane acrylate oligomer mayalso contain a polyether structure that assists in overcoming theproblem of oxygen inhibition of the free-radical polymerization process.This contributes to faster curing of the ink composition at lower energyand power levels. In certain embodiments, the polyester acrylateoligomer is a mercapto modified polyester acrylate. An exemplarymercapto modified polyester acrylate is EBECRYL LED 02, from Allnex. Incertain embodiments of the present invention, the oligomer systemcomprises from about 10% to about 40% by weight, from about 15% to about35% by weight, or from about 20% to about 30% by weight of the inkcomposition. When present in certain embodiments, the total urethaneacrylate oligomer comprises from about 5% to about 25% by weight, fromabout 7.5% to about 20%, or from about 10% to about 17% by weight of theink composition. In certain embodiments, when present, the mercaptomodified polyester acrylate is present within the ink composition at alevel of from about 2.5% to about 20% by weight, from about 5% to about15% by weight, or from about 7.5% to about 12.5% by weight of the inkcomposition.

In certain embodiments, the ink composition may comprise an acrylatepolymer resin. In particular embodiments, the acrylic resin(s) maycomprise methyl(meth) acrylates, ethyl(meth) acrylates, butyl(meth)acrylates, and copolymers thereof. The resins may exhibit glasstransition temperatures (Tg) between the range of about −40° C. to about80° C., between about −20° C. to about 60° C., or between about 0° C. toabout 55° C. An exemplary acrylate polymer resin is ELVACITE 2016, amethyl methacrylate/n-butyl methacrylate copolymer from Lucite (MW=about60,000 and Tg=59° C.). In certain embodiments, higher molecular weightresins are preferred. In those embodiments, the resins exhibit molecularweights of at least 10,000, at least 20,000, or at least 40,000. Inother embodiments, the resins exhibit molecular weights of between about7,000 to about 100,000, or between about 25,000 to about 85,000, orbetween about 40,000 to about 70,000 g/mol. In certain embodiments, thetotal acrylic polymer resin content of the ink formulations is fromabout 5% to about 25% by weight, from about 7.5% to about 20% by weight,or from about 10% to about 15% by weight of the ink composition.

Ink formulations may also include one or more pigments. In certainembodiments, the inks use pigments as the only colorant and do notcontain any dyes. Pigment levels employed will vary somewhat dependingupon the color of the ink. However, in particular embodiments, inkformulations according to the present invents comprise pigments at alevel of between about 1% to about 25% by weight, between about 2% toabout 20% by weight, or between about 3% to about 15% by weight. It isalso within the scope of the present invention to provide unpigmented orclear coatings.

In certain embodiments, the photoinitiator system comprises one or moremembers selected from the group consisting of phosphine oxidephotoinitiators, ketone photoinitiators, and titanocene photoinitiators.In preferred embodiments, the photoinitator system comprises at leastone of each of the aforementioned photoinitiator classes. It is alsowithin the scope of the present invention for the photoinitiator systemto further comprise an amine co-initiator. In certain embodiments, thephotoinitiator system comprises a mixture of at least three, at leastfour, or at least 5 separate photoinitiators taken from the foregoingphotoinitiator types. The photoinitiators are selected based upon theiractivity across certain targeted wavelength ranges at certain energylevels. In addition to being effective in adsorbing light in the UVAspectrum, the photoinitiator system utilized in the present inventionhas also been found to be quite reactive in the blue and green portionof the spectrum (between 450 to 570 nm) which greatly helps the broadband curing range of the ink. This broad band cure range allows for thescavenging of other, previously unused, portions of the light spectrumemitted from the curing lamps. Exemplary wavelengths over which thevarious photoinitiators are particularly active are from about 320 toabout 450 nm, from about 360 to about 425 nm, or from about 380 to about410 nm. In certain embodiments, the photointiators are particularlyeffective in adsorbing light in the UVA spectrum.

Photoinitiator selection also depends to some degree on the intendedcolor of the ink formulation. If the ink formulation is to be white,then photoinitiators that have a tendency to cause yellowing of the inkshould be avoided. However, if the ink is to be colored, yellowing isless of a concern and a broader variety of photoinitiators may beemployed. In one embodiment, the photoinitiator system comprises one ormore phosphine oxide photoinitiators, one or more ketonephotoinitiators, one or more titanocene photointiators, and one or moreamine-based photoinitators. In particular embodiments, thephotoinitiator system comprises from about 2% to about 12% by weight,from about 4% to about 10% by weight, or between about 4.5% to about 7%by weight of the ink formulation.

Exemplary phosphine oxide photoinitiators include2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (TPO photoinitiator) andbis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (available as IRGACURE819 from BASF). The phosphine oxide photoinitiators may also be providedas liquids in the form of monomer dispersions and solutions. Thephosphine oxide photoinitiator may be present in the ink composition ata level of from about 0.5% to about 5% by weight, from about 1% to about3%, or from about 1.25% to about 2.25% by weight.

Exemplary ketone photoinitiators include2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 (IRGACURE369), 2-isopropylthioxanthone (ITX), 1-hydroxy-cyclohexyl-phenyl-ketone(IRGACURE 184), camphorquinone,2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one (IRGACURE907), 2,2-dimethoxy-1,2-diphenylethan-1-one (IRGACURE 651),benzophenone, 2,4-diethylthioxanthone (DETX), and benzildimethylketal(ESACURE 1). The ketone photoinitiator may be present in the inkcomposition at a level of from about 0.75% to about 7.5% by weight, fromabout 1.5% to about 6% by weight, or from about 2.5% to about 4.5% byweight. In certain embodiments, at least two ketone photoinitiators areused in the ink formulation.

An exemplary titanocene photoinitator includesbis(η-5-2,4-cylcopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium (IRGACURE 784). The titanocene photoinitiator may be present inthe ink composition at a level of from about 0.01% to about 2.5% byweight, from about 0.1% to about 1.5% by weight, or from about 0.25% toabout 1% by weight of the ink composition.

Exemplary amine-based photoinitiators include methyldiethanolamine(MDEA), amine acrylates (EBECRYL 7100), triethanolamine, copolymerizableamine (EBECRYL P115), acrylated amine (EBECRYL P104), and reactive amineco-initiators (CN 373). In certain embodiments, the ink compositioncomprises at least two amine-based photoinitiators. The amine-basedphotoinitiators may be present in the ink composition at a level of fromabout 0.5% to about 8% by weight, from about 1.5% to about 6.5% byweight, or from about 3% to about 5% by weight. In certain embodiments,higher amine values are preferred. Particularly amine values betweenabout 90 to about 400, or between about 120 to about 350, or betweenabout 150 to about 320 are preferred.

The ink formulations may include a number of other, optional componentssuch a stabilizers, surfactants, fragrances, defoaming agents,suspension agents, and flow additives. These additional components aregenerally present in ink formulations at a level of less than 5% byweight each, less than 2.5% by weight each, or less than 1% by weighteach. In certain embodiments, the ink compositions comprise fumed silica(e.g., AEROSIL 200) in an amount of from about 0.5% to about 6% byweight, from about 1% to about 5% by weight, or from about 2% to about4% by weight of the ink composition. In certain embodiments, the inkformulations may further comprise an amide wax (e.g., CERAFLOUR 988micronized amide wax) in an amount of from about 0.5% to about 6% byweight, from about 1% to about 5% by weight, or from about 2% to about4% by weight of the ink composition.

The coating composition may also comprises one or more antimicrobialagents. Generally, any antimicrobial agent may be used with the coatingcompositions described herein. However, certain embodiments of thepresent invention utilize silver-based antimicrobial agents. Suchsilver-based antimicrobial agents may comprise metallic silver (i.e.,zero valence atoms) or silver ions. Exemplary silver-based antimicrobialagents include Ionpure™, a soluble glass containing antimicrobial silverions, available from Ishizuka Glass, Iwakura-shi, Japan, Biomaster™ fromAddmaster (UK) Ltd., Agion from Agion Technologies, Wakefield, Mass.,and BASF Iraguard B Silver. In certain embodiments, the antimicrobialagent is provided as a solid, particularly as a powder, that can bedissolved or suspended in the ink composition.

In those embodiments in which an antimicrobial agent is present, thecoating exhibits germicidal properties. The germicidal properties of thecoating composition make it particularly suited for use in applicationswhere sanitary conditions are highly desirable such as in restaurants,hospitals, schools, and food and beverage processing facilities. Inthese applications, the coating composition may be applied to walls,food handling surfaces, and the like. Not only will surfaces having thecoating applied thereto resist staining, but the surface itself iscapable of killing microbes coming into contact therewith. The coatingcompositions are particularly suited for protecting surfaces fromcontamination with one or more, and in some embodiments all, of thefollowing pathogens: K. pneumoniae, Methicillin Resistant S. aureus(MRSA), Clostridium difficile, S. epidermidis, A. baumannii, C.albicans, E. coli, P. aeruginosa, S. aureus, Enterococcus spp. (e.g.,Vancomycin Resistant Enterococcus faecalis (VRE)), Candida spp., andCoNS. In particular embodiments, the coating compositions inhibit thegrowth of one or more, and preferably all, of the foregoing pathogenswhen tested according to AATCC Test Method 147. In still otherembodiments, the coating composition is able to provide greater than a3-log reduction in the levels of at least one, and preferably all, ofthe foregoing pathogens when tested according to Japanese IndustrialStandard (JIS) Z 2801. In yet other embodiments, the coating compositionis able to provide greater than a 4-log reduction, or even greater thana 5-log reduction, in one or more of the foregoing pathogens.

The viscosity of ink formulations according to the present inventiondepend to some degree on the type of printing press with which the inkwill be used. If the ink is to be used with a roller coating press, theink viscosity may be between about 200 to about 800 cps. If the ink isto be used with a flexographic printing press, the ink viscosity may bebetween about 200 to about 1000 cps. If the ink is to be used with ascreen printing press, the ink viscosity may be between about 1000 cpsto about 4000 cps. If the ink is to be used with a lithographic printingpress, the ink will have a viscosity of greater than 4000 cps. Allviscosities expressed herein are measured at 25° C. using a Brookfieldviscometer.

The present invention also provides methods for printing an ink imageonto a substrate. As noted above, the printing press utilized can be anytype of printing press including a screen-printing press, or aflexographic printing press. The ink utilized with the printing pressmay be any UV-curable ink as described herein and is specificallyformulated for a particular type of printing press.

Likewise, the substrate upon which the ink is applied may comprise anynumber of materials, including synthetic resin materials, glass,ceramic, metal, paper, and other natural and synthetic fibrousmaterials. Exemplary materials that can be used as substrates includepolypropylene, polyethylene, polyethylene terephthalate, styrene, vinyl,polycarbonate, acrylic, cardboard, and TYVEK. The substrate may comprisesheets, webs or other thin films. In alternate embodiments, thesubstrate can be in the form of a finished product such as a container,and particularly a bottle. Because the light source operates in areduced-power mode, significantly less heat is generated therebyenabling the substrate to comprise heat sensitive materials such asflexographic thin films, polyolefin films, and bioxy-orientedpolypropylene (BOPP) films, which heretofore would have been damaged bythe lamps operating at their full power setting.

In certain embodiments, the present invention is directed towardprinting images on bottles, especially bottles made from synthetic resinmaterial such as polyethylene, polypropylene, and PET. In someembodiments, bottle formation and printing occurs in immediatesuccession. In those embodiments, the bottle is blow molded from ablank, flame treated and imprinted with the ink image. In particularembodiments, the flame treatment and printing occur in very closeproximity with both operations occurring within one and one-halfrevolutions of the bottle.

Once the ink has been deposited onto the substrate, the substrate ispassed through a curing station having at least one lamp capable ofemitting UV light in the 280-310 nm wavelength range and directing thatUV light toward the substrate containing the printed ink image. Incertain embodiments, the lamp is a mercury vapor lamp, but other typesof lamps may be used such as a microwave-powered, electrodeless fusionlamp. The curing station may further comprise a reflector that helps tofocus light emitted by the lamp onto the substrate.

In certain embodiments, the lamp has a nominal or rated wattage of atleast 200 W, and preferably from about 200 W to about 300 W. The curingstation may also feature a standby mode, which is a reduced powersetting maintains lamp readiness for full illumination. In certainembodiments, the standby mode operates the lamp at 50% or less of itsrated power. In other embodiments, the curing station may offercontinuously adjustable power from 25% to 100%. In embodiments of thepresent invention, the lamp, having a rated wattage of at least 200 W,is operated at 50% or below, at 40% or below, or at 25% or below of itsrated wattage while the printed substrate is passed through the curingstation. Beneath the lamps is a conveyor system, such as a belt conveyorsystem, upon which the substrate bearing the printed ink image may beplaced. The conveyor system carries the substrate past the curingstation's lamp(s) at a preselected rate. In certain embodiments, theconveyor may operate at a speed of at least 50 linear feet per minute,at least 75 linear feet per minute, at least 100 linear feet per minute,or at least 125 linear feet per minute. In particular embodiments, theconveyor operates at a speed of from about 50 to about 250 ft/min, fromabout 100 to about 200 ft/min, or from about 125 to about 175 ft/min.

The selection of lamp power and conveyor speed, among other factors,directly affects the amount of radiant energy and radiant power thatimpinges upon the substrate during its passage through the curingstation. In certain embodiments, the step of passing the printedsubstrate through the curing station exposes the ink composition printedthereon to a radiant energy level of from about 30 to about 125 mJ, orfrom about 50 to about 100 mJ, or from about 65 to about 85 mJ. Incertain embodiments, the step of passing the printed substrate throughthe curing station exposes the ink composition printed thereon to aradiant power level of from about 400 to about 800 mW, from about 450 toabout 750 mW, or from about 500 to about 700 mW. The ink image printedon the substrate emerges from the curing station fully cured.

In certain embodiments, ink compositions according to the presentinvention have excellent adhesion characteristics as determined by ASTMD3359-08 Standard Test Methods for Measuring Adhesion by Tape Test.Generally, this test method involves applying a layer of the ink to aparticular substrate creating a lattice pattern of cuts in the curedink, applying a pressure-sensitive tape over the lattice, and removingthe lattice. Performance is then judged by how much, if any, of the inkwas removed from the lattice by the tape. In particular embodimentsaccording to the present invention, less than 5% of the ink is removedby the tape, and more preferably, none of the ink is removed by thetape. In this particular test, the ink is deposited on the substrate toform a film of at least 0.5 mil thickness. The substrate used in theadhesion test may vary from rigid plastic substrates like polyethylene,polycarbonate, corrugated polyethylene, PET, HDPE, flexible vinyl filmssuch as those used for vehicle wraps, and metallic substrates. It isnoted that for the purposes of the physical performance tests describedherein (e.g., various adhesion and resistance tests), a pigment, dye orother colorant may be added to the coating composition to aid visualinspect of the coating's performance.

In certain embodiments of the present invention, the ink compositionsalso exhibit excellent resistance to a variety of aggressive solventsand chemicals such as acetone, paint thinners, alcohols, and acids.Specifically, the ink composition can be tested in accordance with ASTMD5402, incorporated by reference herein, and withstand at least 10, oreven at least 50, rubs with a cloth or wad of cotton soaked withacetone, ethyl alcohol, or isopropyl alcohol without showing visiblesigns of the ink being removed from the substrate.

Adhesion to a variety of substrates is also evidenced in thatsubstrates, and particularly bottles made of HDPE and PET, printed withink compositions as described herein exhibit excellent washingcharacteristics. In certain embodiments, substrates bearing a printedimage can withstand at least 100 washing cycles without visible imagewear or degradation. As certain bottles are intended for use ascontainers for soaps and shampoos, it is very important that the printedimage not be degraded upon exposure to the various surfactants andcaustic materials present in those products.

Synthetic resin material bottles, such as HDPE and PET bottles, areoften squeezed in order to deliver product from the bottle. In thisrespect, it is another important feature that the image printed thereonbe capable of flexing with the bottle without visible signs of crackingor flaking off the bottle. In one such flex test, HDPE or PET bottlesare immersed in water for 10 minutes. The bottle is flexed back andforth, simulating squeezing of product form the bottle, six times. Thebottle is then visually inspected for signs of image degradation. Inpreferred embodiments, the bottles should exhibit no visible signs ofimage degradation, such as ink cracking or flaking from the bottle.

EXAMPLE

The following Example sets forth exemplary magenta and yellow screenprinting ink compositions made in accordance with the present invention.Both inks are made employing a base varnish formulation, which isdescribed in Table 1. The varnish is then mixed with the othercomponents to form the finished ink composition. The exemplary inkformulations are described in Table 2.

TABLE 1 Varnish Formulation Wt. % Trimethylolpropane triacrylate 5(TMPTA) (Sartomer) 1,6 Hexanediol diacrylate 31.4 (HDODA) (Sartomer)2-Phenoxyethyl acrylate (Sartomer) 33 MEHQ, stabilizer, (FIRST-CURE 1.3ST-1) (Archway) Fragrance (Agilex) 0.3 ELVACITE 2016, methyl 29methacrylate/n-butyl methacrylate copolymer (Elvacite 2016)(Lucite)

TABLE 2 Magenta Yellow Component Wt. % Wt. % Varnish 43.8 44.15 1,6Hexanediol diacrylate 5 5 (HDODA) (Sartomer) Red pigment (Clariant) 2 —Red pigment (BASF) 2.2 — Hanza brilliant yellow pigment — 0.75 Permanentyellow GG pigment (Clariant) — 1.95 3G/FGL yellow pigment — 2.25 AEROSIL200, fumed silica (Brenntag) 3 2.35 CN 983, urethane acrylate oligomer(Sartomer) 5 5 2-Phenoxyethyl acrylate (Sartomer) 5 5 FOAMEX N, defoamer(Tego) 0.7 0.7 CRU FLUID 350, polydimethylsiloxane 0.6 0.6 antifoamsilicone fluid (Crucible) Methyl diethanolamine (MDEA) (Brenntag) 0.20.2 CN 373, reactive amine co-initiator (Sartomer) 4 42-isopropylthioxanthone (ITX), photoinitiator 3 3 (Biddle)Bis(2,4,6-trimethylbenzoyl)- 1.5 1.5 phenylphosphineoxide (IRGACURE819), photoinitiator (BASF) 2-Benzyl-2-dimethylamino-1-(4- 0.5 0.5morpholinophenyl)-butanone-1 (IRGACURE 369), photoinitiator (BASF)Difunctional aliphatic urethane acrylate 10 10 (EBECRYL 8811), oligomer(Allnex) Bis(η-5-2,4-cylcopentadien-1-yl)-bis(2,6- 0.5 0.05difluoro-3-(1H-pyrrol-1-yl)-phenyl) titanium (IRGACURE 784),photoinitiator (BASF) Mercapto modified polyester acrylate resin 10 10(EBECRYL LED 02) (Allnex) Micronized amide wax (CERAFLOUR 988) 3 3 (BYKChemie)

The ink formulations were tested for curing characteristics uponexposure to a 200 W SPE UV mercury vapor lamp operating at 50% intensity(i.e., 100 W power setting). Leneta test cards bearing a samplescreen-printed image were prepared and passed under the lamp at a linearspeed of 50 feet per minute and 119 feet per minute. A photometer wasused to measure the energy and power to which the test cards wereexposed during each pass. At a rate of 50 ft/min, the test cards wereexposed to 185 mJ and 586 mW. At a rate of 119 ft/min, the test cardswere exposed to 75 mJ and 441 mW. In both cases, the ink image was fullycured following passage underneath the mercury vapor lamp.

The ink formulations were also tested for curing characteristics uponexposure to a 300 WPI Fusion UV lamp operating at 50% intensity. Lenetatest cards bearing a smaple screen-printed image were prepared andpassed under the lamp at a linear speed of 130 ft/min and 220 ft/min. Aphotometer was used to measure the energy and power to which the testcards were exposed during each pass. At a rate of 130 ft/min, the testcards were exposed to 70 mJ and 859 mW. At a rate of 220 ft/min, thetest cards were exposed to 38 mJ and 481 mW. In both cases, the inkimage was fully cured following passage underneath the Fusion lamp.

I claim:
 1. A UV-curable ink composition comprising: a monomer systemcomprising at least one monofunctional monomer and at least onemultifunctional monomer; an oligomer system comprising at least oneurethane acrylate oligomer and at least one mercapto modified polyesteracrylate; an acrylate polymer resin; a pigment; and an initiator systemcomprising at least one phosphine oxide photoinitiator, at least oneketone photoinitiator, at least one titanocene photoinitator and atleast one amine co-initiator, wherein said UV-curable ink composition iscapable of being cured by exposure to UV light emitted from a lampoperating at 100 W or less at a line speed of at least 50 ft/min.
 2. TheUV-curable ink composition of claim 1, said UV-curable ink compositionfurther comprising fumed silica.
 3. The UV-curable ink composition ofclaim 1, said UV-curable ink composition further comprising methyldiethanolamine (MDEA).
 4. The UV-curable ink composition of claim 1,wherein said monomer system is comprised of mono-, di-, andtrifunctional acrylate monomers.
 5. The UV-curable ink composition ofclaim 1, wherein acrylate polymer resin is a methyl methacrylate/n-butylmethacrylate copolymer resin.
 6. The UV-curable ink composition of claim1, wherein said monomer system comprises from about 20% to about 60% byweight of said UV-curable ink composition.
 7. The UV-curable inkcomposition of claim 1, wherein said oligomer system comprises fromabout 10% to about 40% by weight of said UV-curable ink composition. 8.The UV-curable ink composition of claim 1, wherein said initiator systemcomprises from about 2% to about 12% by weight of said UV-curable inkcomposition.
 9. The UV-curable ink composition of claim 1, saidUV-curable ink composition comprising an amide wax.
 10. A method forcreating an article having a printed ink image thereon comprising thesteps of: printing an ink image onto a substrate using a UV-curable inkcomposition to form a printed substrate, said UV-curable ink compositioncomprising— a monomer system comprising at least one monofunctionalmonomer and at least one multifunctional monomer; an oligomer systemcomprising at least one mercapto modified polyester acrylate; and aninitiator system comprising one or more members selected from the groupconsisting of phosphine oxide photoinitiators, ketone photoinitiators,and titanocene photoinitators; passing said printed substrate through acuring station at a rate of at least 50 linear feet per minute to formsaid article, said curing station comprising at least one lamp that hasa rated wattage of at least 200 W, said lamp being operated at 50% orbelow of its rated wattage while said printed substrate is being passedthrough said curing station.
 11. The method of claim 10, wherein saidmonomer system is comprised of mono-, di-, and trifunctional acrylatemonomers.
 12. The method of claim 10, wherein said monomer systemcomprises from about 20% to about 60% by weight of said UV-curable inkcomposition.
 13. The method of claim 10, wherein said oligomer systemfurther comprises at least one urethane acrylate oligomer.
 14. Themethod of claim 10, wherein oligomer system comprises between about 10%to about 40% by weight of said UV-curable ink composition.
 15. Themethod of claim 10, wherein said initiator system comprises betweenabout 2% to about 12% by weight of said UV-curable ink composition. 16.The method of claim 10, wherein said lamp comprises a mercury-vaporlamp.
 17. The method of claim 10, wherein said step of passing saidprinted substrate through a curing station exposes said ink compositionto an energy level of from about 30 to about 125 mJ.
 18. The method ofclaim 10, wherein said step of passing said printed substrate through acuring station exposes said ink composition to a power level of fromabout 400 to about 800 mW.
 19. A UV-curable ink composition comprising:a monomer system comprising at least one monofunctional monomer and atleast one multifunctional monomer; an oligomer system comprising atleast one urethane acrylate oligomer and at least one mercapto modifiedpolyester acrylate; an acrylate polymer resin; a pigment; an initiatorsystem comprising at least one phosphine oxide photoinitiator, at leastone ketone photoinitiator, at least one titanocene photoinitator and atleast one amine co-initiator; and fumed silica.
 20. A UV-curable inkcomposition comprising: a monomer system comprising at least onemonofunctional monomer and at least one multifunctional monomer; anoligomer system comprising at least one urethane acrylate oligomer andat least one mercapto modified polyester acrylate; an acrylate polymerresin; a pigment; an initiator system comprising at least one phosphineoxide photoinitiator, at least one ketone photoinitiator, at least onetitanocene photoinitator and at least one amine co-initiator; and methyldiethanolamine (MDEA).
 21. A UV-curable ink composition comprising: amonomer system comprising at least one monofunctional monomer and atleast one multifunctional monomer; an oligomer system comprising atleast one urethane acrylate oligomer and at least one mercapto modifiedpolyester acrylate; a methyl methacrylate/n-butyl methacrylate copolymerresin; a pigment; and an initiator system comprising at least onephosphine oxide photoinitiator, at least one ketone photoinitiator, atleast one titanocene photoinitator and at least one amine co-initiator.